IPAC2019 - Classification: MC3: Novel Particle Sources and Acceleration Techniques / T02 Electron Sources

Paper	Title	Page
TUXPLS1	MeV Ultrafast Electron Diffraction and Microscopy for the Scientific Frontier
	D. Xiang Shanghai Jiao Tong University, Shanghai, People’s Republic of China
	Historically particle accelerators are instrumental for high energy physics (accelerator based colliders) and photon science (accelerator based synchrotron source and FELs). Now there is growing interest in applying accelerator technology to solve the grand challenges in probing matter at ultrafast temporal and ultrasmall spatial scales. In this talk I will discuss how one can use MeV electrons produced in accelerators to study ultrafast dynamics at atomic scale through ultrafast electron diffraction and microscopy techniques. This is made possible with the recent progress both in ultrafast lasers and in the generation and control of high-brightness electron beams used in modern accelerators. I will focus on advanced techniques such as THz streaking and THz compression that may push the resolution to the attosecond regime. Complementary to x-ray FELs, such facility is expected to enable access to new sciences by giving researchers unparalleled power and precision in examining the fundamental nature of matter. A comparison of performance reach to other methods is included.
	Slides TUXPLS1 [15.371 MB]
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TUXXPLS1	SRF Gun with Warm Photocathode
	I. Pinayev, I. Ben-Zvi, J.C. Brutus, T. Hayes, Y.C. Jing, V. Litvinenko, J. Ma, K. Mihara, G. Narayan, F. Severino, K. Shih, J. Skaritka, E. Wang, G. Wang BNL, Upton, Long Island, New York, USA I. Petrushina SUNY SB, Stony Brook, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The 113 MHz superconducting gun is used an electron source for the coherent electron cooling experiment. The unique feature of the gun is that a photocathode is held at room temperature. It allowed to preserve the quantum efficiency of Cs2KSb cathode which is adversely affected by cryogenic temperatures. Relatively low frequency permitted fully realize the accelerating field gradient what in in turn helps to achieve 10 nC charge and 0.3 microns normalized emittance. We present the achieved performance an operational experience as well.
	Slides TUXXPLS1 [6.786 MB]
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TUPTS013	Characterization of an Electron Gun Test Setup Based on Multipacting	1961
	C. Henkel, W. Hillert, V. Miltchev University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany K. Flöttmann DESY, Hamburg, Germany
	A multipacting electron gun (MEG) is a micro-pulse electron source, based on secondary electron emission in a resonant microwave cavity structure, for the generation of low emittance electron bunches in continuous wave operation. Based on numerical simulations, an experimental test setup for low-energy electron beams at 3 GHz has been established. In this contribution we show a detailed description and characterization of the RF test stand, supported by first results on charge collection measurements of the output current with respect to important operational parameters like power transmission and modifiable mechanical dimensions in the assembly of the experiment. This is a milestone in the development of a MEG setup for higher energetic electron beams and subsequent investigation of essential beam characteristics like emittance and energy distribution for the optimization with regard to best possible beam quality and future fields of application.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS013
About •	paper received ※ 30 April 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPTS024	Design of a Full C-Band Injector for Ultra-High Brightness Electron Beam	1979
	D. Alesini, F. Cardelli, G. Castorina, M. Croia, M. Diomede, M. Ferrario, A. Gallo, A. Giribono, B. Spataro, C. Vaccarezza, A. Vannozzi INFN/LNF, Frascati (Roma), Italy
	High gradient rf photo-injectors have been a key development to enable several applications of high quality electron beams. They allow the generation of beams with very high peak current and low transverse emittance, satisfying the tight demands for free-electron lasers, energy recovery linacs, Compton/Thomson sources and high-energy linear colliders. In the paper we present the design of a new full C-band RF photo-injector recently developed in the framework of the XLS-Compact Light design study and of the EuPRAXIA@SPARC_LAB proposal. It allows to reach extremely good beam performances in terms of beam emittance (at the level of few hundreds nm), energy spread and peak current. The photo-injector is based on a very high gradient (>200 MV/m) ultra-fast (RF pulses <200 ns) C-band RF gun, followed by two C band TW structures. Different types of couplers for the 1.6 cell RF gun have been considered and also a new compact low pulsed heating coupler working on the TM020 mode on the full cell has been proposed. In the paper we report the design criteria of the gun, the powering system, and the results of the beam dynamics simulations. We also discuss the case of 1 kHz repetition rate.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS024
About •	paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPTS054	1st+2nd Harmonic Photocathode Bimodal Gun R&D	2054
SUSPFO086	use link to see paper's listing under its alternate paper code
	L. Wang SINAP, Shanghai, People’s Republic of China W. Fang, Z.T. Zhao SSRF, Shanghai, People’s Republic of China J.L. Hirshfield Yale University, Physics Department, New Haven, CT, USA J.L. Hirshfield, S.V. Shchelkunov Omega-P, Inc., New Haven, Connecticut, USA Y. Jiang, S.V. Shchelkunov Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA L. Wang University of Chinese Academy of Sciences, Beijing, People’s Republic of China
	Funding: U.S. Dept. of Energy A novel Bimodal Electron Gun is designed to apply microwaves at two harmonically-related frequency in a 0.6 cell RF gun to increase the RF breakdown threshold and enhance the beam quality. This stratagem is intended to allow the RF gun structure to support a high accelera-tion gradient as well as to manipulate the emittance evolution in the half cell. By selecting a proper ampli-tude ratio and phase relationship between the first and second harmonic RF field components in the gun cavity, the superposition of the harmonic field components can provide a flat-top like RF profile to omitting the RF emittance component in the gun, while increase the RF breakdown threshold. The recent status of the Bimodal Electron Gun R&D is presented, including the designs of the novel two frequency RF structure and the simulation of the beam dynamic.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS054
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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TUPTS069	A Plasmonic Niobium Photocathode for SRF Gun Applications	2079
	F.E. Hannon JLab, Newport News, Virginia, USA G. Andonian, L.H. Harris RadiaBeam, Marina del Rey, California, USA
	The typical quantum efficiency of niobium is of the order 10^-4, whilst also requiring UV lasers for emission. This paper presents the results of a plasmonic niobium surface that operates with IR laser via multiphoton emission.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS069
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPTS070	Systematic Benchmarking of a Planar (N)UNCD Field Emission Cathode	2083
	J.H. Shao, M.E. Conde, W. Liu, J.G. Power, E.E. Wisniewski ANL, Argonne, Illinois, USA S.V. Baryshev, M.S. Schneider Michigan State University, East Lansing, Michigan, USA G. Chen IIT, Chicago, Illinois, USA K. Kovi Euclid TechLabs, LLC, Solon, Ohio, USA L.K. Spentzouris Illinois Institute of Technology, Chicago, Illinois, USA
	Planar nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, is a unique and attractive field emission source because of the capability to generate high charge beam, the simplicity of production without shaped emitters, and the ease of handling with moderate vacuum requirement. In the presented study using an L-band normal conducting single-cell rf gun, a (N)UNCD cathode has been conditioned to 42 MV/m with a well-controlled manner and reached a maximum charge of 15 nC and an average emission current of 6~mA during a 2.5 us emission period. The systematic study of emission properties during the rf conditioning process illustrates the tunability of (N)UNCD in a wide range of surface gradients. This research demonstrates the versatility of (N)UNCD cathode which could enable multiple designs of field emission rf injector for industrial and scientific applications.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS070
About •	paper received ※ 20 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPTS073	Analysis of Electron Beam Divergence in Diamond Field Emitter Array Cathodes	2090
	D. Kim, H.L. Andrews, R.L. Fleming, C. Huang, J.W. Lewellen, K.E. Nichols, V.N. Pavlenko, E.I. Simakov LANL, Los Alamos, New Mexico, USA B.K. Choi Cheju Halla University, Jeju-si, Republic of Korea
	Funding: Los Alamos National Laboratory (LANL) Laboratory Directed Research and Development (LDRD) program (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-NA-0003525). At Los Alamos National Laboratory (LANL), we have recently established a capability to fabricate diamond array cathodes for electron beam sources. Our fabricated diamond field emitter arrays (DFEAs) are the arrays of micrometer-scale diamond pyramids with nanometer-scale sharp tips and produce high per-tip current (> 15 μA per-tip) in DC testing. For the beam divergence measurements, we designed and assembled a test stand consisting of a DFEA cathode, a mesh aperture of 0.375-inch for an anode, and AZO (ZnO:Al2O3) screen coated on a sapphire substrate for beam visualization. A negative voltage of about 40 kV is applied to the cathode, and the mesh and the screen are kept at ground. We measure a size of the electron beam on the AZO screen at different mesh to screen distances at a fixed cathode-mesh gap in order to calculate the beam divergence angles. We also perform the beam dynamics simulations with Computer Simulation Technology (CST) Studio and General Particle Tracer (GPT) using a single pyramidal shape with a nanowire tip model. In this presentation, the measured experimental results of the beam divergences will be compared to the beam dynamic simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS073
About •	paper received ※ 14 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPTS077	Design of a High Gradient THz-Driven Electron Gun	2098
SUSPFO127	use link to see paper's listing under its alternate paper code
	S.M. Lewis, V.A. Dolgashev, A.A. Haase, E.A. Nanni, M.A.K. Othman, A.V. Sy, S.G. Tantawi SLAC, Menlo Park, California, USA D. Kim, E.I. Simakov LANL, Los Alamos, New Mexico, USA
	Funding: This work was supported by Department of Energy contract DE-AC02-76SF00515. This work was also supported by NSF grants PHY-1734015. We present the design of a high-gradient electron gun. The goal of this gun is to generate relativistic electrons using GV/m accelerating fields. The initial design is a standing-wave field-emission gun operating in the pi-mode with a cavity frequency of 110.08 GHz. A pulsed 110 GHz gyrotron oscillator will be used to drive the structure with power coupled in through a TM01 circular waveguide mode. The gun is machined in two halves which are bonded. This prototype will be used to characterize the electron beam and study RF breakdown at 110 GHz.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS077
About •	paper received ※ 14 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPTS079	Overcoming Multipacting Barriers in SRF Photoinjectors	2105
	I. Petrushina SUNY SB, Stony Brook, New York, USA V. Litvinenko, G. Narayan, I. Pinayev, F. Severino, K.S. Smith BNL, Upton, Long Island, New York, USA V. Litvinenko Stony Brook University, Stony Brook, USA
	Superconducting RF (SRF) photoinjectors are considered to be a potential breakthrough in the area of high brightness electron sources. However, there is always the very important question of the compatibility of SRF cavities and high quantum efficiency (QE) photocathodes. A deposition of active elements from high QE photocathodes on the surface of a cavity makes it more vulnerable to multipacting (MP) and could affect the operation of an SRF gun. On the other side, MP can significantly reduce the lifetime of a photocathode. It is well known in the SRF community that a strong coupling, high forward power and sufficient cleanliness of cavity walls are the key components to overcome a low-level MP zone. In this paper we present a theoretical model of passing a MP barrier which could help estimate the desirable conditions for successful operation of an SRF gun. We demonstrate our results for the 113 MHz SRF photo-injector for Coherent electron Cooling (CeC) alongside with the experimental observations and 3D simulations of the MP discharge in the cavity. The results of the theoretical model and simulations show good agreement with the experimental results, and demonstrate that, if approached carefully, MP zones can be easily passed without any harm to the photocathode.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS079
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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TUPTS083	Simulations and Experimental Plans for a High-Repetition-Rate Field-Enhanced Conduction-Cooled Superconducting RF Electron Source	2113
SUSPFO047	use link to see paper's listing under its alternate paper code
	O. Mohsen, A. McKeown, D. Mihalcea, P. Piot, I. Salehinia Northern Illinois University, DeKalb, Illinois, USA R. Dhuley, M.G. Geelhoed, D. Mihalcea, P. Piot, J.C.T. Thangaraj Fermilab, Batavia, Illinois, USA
	Funding: Work supported by DOE awards DE-SC0018367 with NIU and DE-AC02-07CH11359 with Fermilab. We present a novel RF design for a field enhanced electron source driven by field emission cathodes. The proposed electron source relies on the enhanced high electric field gradients at the cathode to simultaneously extract and accelerate electrons. The system will be tested in a conduction-cooled superconducting radio-frequency cavity recently demonstrated at Fermilab. In this paper, we present electromagnetic and thermal simulations of the setup that support the feasibility of the design.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS083
About •	paper received ※ 18 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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TUPTS084	Performances of Silicon-Based Field-Emission Cathodes Coated with UltraNano Crystalline Diamond	2117
	O. Mohsen, V. Korampally, A. Lueangaramwong, P. Piot, V. Valluri Northern Illinois University, DeKalb, Illinois, USA R. Divan, A.V. Sumant Argonne National Laboratory, Argonne, Illinois, USA P. Piot Fermilab, Batavia, Illinois, USA
	Funding: Work supported by NSF grant PHY-1535401 and DOE award DE-SC0018367 with NIU Field-emission electron sources have been considered as possible candidates for the production of bright or high-current electron bunches. In this paper, we report on the experimental characterization of silicon-based field-emitter arrays (FEA) in a DC high voltage gap. The silicon cathodes are produced via a simple self-assembling process. The measurement reported in this paper especially compares the field-emission properties of a nanostructured and planar diamond-coated Si-based cathode.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS084
About •	paper received ※ 17 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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TUPTS088	A Normal Conducting RF Gun as an Electron Source for JLEIC Cooling	2127
	F.E. Hannon, R.A. Rimmer JLab, Newport News, Virginia, USA
	The baseline design for a magnetized injector for the bunched-beam electron cooler ring, as part of the Jeffer-son Lab Electron Ion Collider (JLEIC) uses a DC photo-cathode electron gun as the source. A challenging aspect of this concept is transporting a 3.2nC electron bunch at low energy and preserving the angular momentum. An RF gun source has been investigated to gauge the potential advantages of high gradient on the photocathode and higher exit energy. The design is presented and compared with the baseline results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS088
About •	paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPTS089	Observations of the Femtosecond Laser-Induced Emission From the Diamond Field Emitter Tips	2130
	E.I. Simakov, H.L. Andrews, R.L. Fleming, D. Kim, V.N. Pavlenko LANL, Los Alamos, New Mexico, USA D.S. Black, K.J. Leedle Stanford University, Stanford, California, USA
	Funding: Los Alamos National Laboratory LDRD Program We present the results of experimental observation of emission from single diamond field emitter tips when triggered by an ultra-short laser pulse. Diamond field emitter array (DFEA) cathodes were originally proposed for applications that require large current densities. DFEAs represent periodic arrays of diamond pyramids with micron-size dimensions and tips with diameters of the order of tens of nanometers. DFEAs are known to produce significant currents in field emission regime under direct current (DC) fields and in radio-frequency (RF) guns. It has been proposed that single diamond tip emitters can be employed for production of small tightly focused electron beams for dielectric laser accelerators (DLAs) that accelerate particles using the energy of light produced by infrared lasers. To generate short electron bunches required by DLAs diamond pyramids may be triggered with a laser. We have recently observed emission produced by a single diamond pyramid when triggered by a laser at different wavelengths from 256 nm to 2020 nm. We have conducted studies with the goal to understand mechanism of the emission. We clearly observed the change in emission mechanism when the wavelength changed from 256 nm to 512 nm. We believe that while the emission at 256 nm is a clear photoemission, the emission at longer wavelengths is likely the field emission caused by intense electric fields of the laser.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS089
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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TUPTS090	Experimental Results of Dense Array Diamond Field Emitters in RF Gun	2134
	K.E. Nichols, H.L. Andrews, D. Kim, E.I. Simakov LANL, Los Alamos, New Mexico, USA S.P. Antipov Euclid Beamlabs LLC, Bolingbrook, USA G. Chen IIT, Chicago, Illinois, USA M.E. Conde, D.S. Doran, G. Ha, W. Liu, J.F. Power, J.H. Shao, C. Whiteford, E.E. Wisniewski ANL, Argonne, Illinois, USA
	We present experimental emission results from arrays of diamond field emitter tips operating in an RF gun at the Argonne Cathode Test-stand. Results from various arrays will be presented with different spacing between array elements. Very high charge densities were produced at various field gradients. The maximum field gradient for a particular geometry was discovered and break-down effects will be presented. Cathode lifetime was preliminarily studied. Further experiments are being planned and work on the cathode design optimization to produce higher quality beams will be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS090
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPTS091	Physics of Electron Beam Generation and Dynamics From Diamond Field Emitter Arrays	2137
	C. Huang, H.L. Andrews, R.C. Baker, R.L. Fleming, D. Kim, T.J. Kwan, V.N. Pavlenko, A. Piryatinski, E.I. Simakov LANL, Los Alamos, New Mexico, USA
	Funding: Work supported by the LDRD program at Los Alamos National Laboratory Many applications such as compact accelerators and electron microscopy demand high brightness electron beams with small beam size and low emittance. Electric-field-assisted diamond emitters manufactured from semiconductor processes are strong candidates for cathodes in such sources. The micro-scale pyramid structure of the emitter has the desirable attribute of significant field enhancement at the sharp interfaces (apex and edges) to facilitate electron emission. We use the LSP particle-in-cell code to simulate the diamond emitter in a diode setup and obtain the beam size and divergence. An empirical fit of the fields around the apex is extracted for detail study. The trend of the beam divergence observed in the simulation is further corroborated using electron’s trajectory in the empirical field model.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS091
About •	paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPTS093	Magnetized Gridded Thermionic Electron Source	2140
SUSPFO122	use link to see paper's listing under its alternate paper code
	M.S. Stefani ODU, Norfolk, Virginia, USA C.M. Gulliford, V.O. Kostroun, C.E. Mayes, K.W. Smolenski Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA F.E. Hannon, M. Poelker, R. Suleiman JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under Contract No. DE-AC05-06OR23177 with the U.S. Department of Energy. The study of magnetized electron beam has become a high priority for its use in ion beam cooling as part of Electron Ion Colliders and the potential of easily forming flat beams for various applications. The demand for high average current for effective ion beam cooling has caused consideration of using bunched magnetized electron beam produced by a gridded thermionic electron gun. This paper presents the design of a potential electron source for JCIEC first measurements characterizing the beam properties of a magnetized thermionic gun.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS093
About •	paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPTS103	The Progress of High Current High Bunch Charge Polarized Electron HVDC Gun	2160
	E. Wang, I. Ben-Zvi, R.F. Lambiase, W. Liu, O.H. Rahman, J. Skaritka, F.J. Willeke BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The high current and high bunch charge polarized electron source is essential for cost reduction of eRHIC. It aims to deliver electron beam with 10 mA average current and 5.3 nC bunch charge. We analyzed the mechanism of cathode degradation and proposed using a large strain superlattice GaAs photocathode in a high voltage DC gun to increase the charge lifetime above kilo Coulomb. The gun has been designed and fabricated and expected to start commissioning by the mid of this year. In this paper, we will present the modeling of ion back bombardment and cathode degrading. We proposed an anode offset scheme to increase cathode lifetime. Also, we will describe the details of gun design and the strategies to demonstrate high current high charge polarized electron beam from this source.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS103
About •	paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPTS104	Spatio-Temporal Shaping of the Photocathode Laser Pulse for Low-Emittance Shaped Electron Bunches	2163
	T. Xu, P. Piot Northern Illinois University, DeKalb, Illinois, USA C.-J. Jing, A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA P. Piot Fermilab, Batavia, Illinois, USA J.G. Power ANL, Argonne, Illinois, USA
	Funding: This work is supported by the U.S. DOE contract No. DE- SC0017750 with Euclid Techlabs LLC., No. DE-SC0018656 with NIU, and No. DE-AC02-06CH11357 with ANL. Photocathode laser shaping techniques to generate temporally shaped electron bunches are appealing owing to their simplicity. Such technique is being considered to form shaped electron bunches to enhance the transformer ratio in beam-driven accelerators. At low energy (i.e. during the emission process) the transverse and longitudinal space charge effects are coupled so that attaining a low beam transverse emittance require the laser to be spatiotemporal shaped. In this paper, we explore the generation of a linearly-ramped bunch with optimized transverse emittance by temporally and radially shaping the laser pulse to provide an adequate initial distribution. We discuss a possible implementation of the optical shaping technique and describe a planned experiment.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS104
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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Paper

Title

Page

TUXPLS1

MeV Ultrafast Electron Diffraction and Microscopy for the Scientific Frontier

D. Xiang
Shanghai Jiao Tong University, Shanghai, People’s Republic of China

Historically particle accelerators are instrumental for high energy physics (accelerator based colliders) and photon science (accelerator based synchrotron source and FELs). Now there is growing interest in applying accelerator technology to solve the grand challenges in probing matter at ultrafast temporal and ultrasmall spatial scales. In this talk I will discuss how one can use MeV electrons produced in accelerators to study ultrafast dynamics at atomic scale through ultrafast electron diffraction and microscopy techniques. This is made possible with the recent progress both in ultrafast lasers and in the generation and control of high-brightness electron beams used in modern accelerators. I will focus on advanced techniques such as THz streaking and THz compression that may push the resolution to the attosecond regime. Complementary to x-ray FELs, such facility is expected to enable access to new sciences by giving researchers unparalleled power and precision in examining the fundamental nature of matter. A comparison of performance reach to other methods is included.

Slides TUXPLS1 [15.371 MB]

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TUXXPLS1

SRF Gun with Warm Photocathode

I. Pinayev, I. Ben-Zvi, J.C. Brutus, T. Hayes, Y.C. Jing, V. Litvinenko, J. Ma, K. Mihara, G. Narayan, F. Severino, K. Shih, J. Skaritka, E. Wang, G. Wang
BNL, Upton, Long Island, New York, USA
I. Petrushina
SUNY SB, Stony Brook, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The 113 MHz superconducting gun is used an electron source for the coherent electron cooling experiment. The unique feature of the gun is that a photocathode is held at room temperature. It allowed to preserve the quantum efficiency of Cs2KSb cathode which is adversely affected by cryogenic temperatures. Relatively low frequency permitted fully realize the accelerating field gradient what in in turn helps to achieve 10 nC charge and 0.3 microns normalized emittance. We present the achieved performance an operational experience as well.

Slides TUXXPLS1 [6.786 MB]

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TUPTS013

Characterization of an Electron Gun Test Setup Based on Multipacting

1961

C. Henkel, W. Hillert, V. Miltchev
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
K. Flöttmann
DESY, Hamburg, Germany

A multipacting electron gun (MEG) is a micro-pulse electron source, based on secondary electron emission in a resonant microwave cavity structure, for the generation of low emittance electron bunches in continuous wave operation. Based on numerical simulations, an experimental test setup for low-energy electron beams at 3 GHz has been established. In this contribution we show a detailed description and characterization of the RF test stand, supported by first results on charge collection measurements of the output current with respect to important operational parameters like power transmission and modifiable mechanical dimensions in the assembly of the experiment. This is a milestone in the development of a MEG setup for higher energetic electron beams and subsequent investigation of essential beam characteristics like emittance and energy distribution for the optimization with regard to best possible beam quality and future fields of application.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS013

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paper received ※ 30 April 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPTS024

Design of a Full C-Band Injector for Ultra-High Brightness Electron Beam

1979

D. Alesini, F. Cardelli, G. Castorina, M. Croia, M. Diomede, M. Ferrario, A. Gallo, A. Giribono, B. Spataro, C. Vaccarezza, A. Vannozzi
INFN/LNF, Frascati (Roma), Italy

High gradient rf photo-injectors have been a key development to enable several applications of high quality electron beams. They allow the generation of beams with very high peak current and low transverse emittance, satisfying the tight demands for free-electron lasers, energy recovery linacs, Compton/Thomson sources and high-energy linear colliders. In the paper we present the design of a new full C-band RF photo-injector recently developed in the framework of the XLS-Compact Light design study and of the EuPRAXIA@SPARC_LAB proposal. It allows to reach extremely good beam performances in terms of beam emittance (at the level of few hundreds nm), energy spread and peak current. The photo-injector is based on a very high gradient (>200 MV/m) ultra-fast (RF pulses <200 ns) C-band RF gun, followed by two C band TW structures. Different types of couplers for the 1.6 cell RF gun have been considered and also a new compact low pulsed heating coupler working on the TM020 mode on the full cell has been proposed. In the paper we report the design criteria of the gun, the powering system, and the results of the beam dynamics simulations. We also discuss the case of 1 kHz repetition rate.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS024

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paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPTS054

1st+2nd Harmonic Photocathode Bimodal Gun R&D

2054

SUSPFO086

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L. Wang
SINAP, Shanghai, People’s Republic of China
W. Fang, Z.T. Zhao
SSRF, Shanghai, People’s Republic of China
J.L. Hirshfield
Yale University, Physics Department, New Haven, CT, USA
J.L. Hirshfield, S.V. Shchelkunov
Omega-P, Inc., New Haven, Connecticut, USA
Y. Jiang, S.V. Shchelkunov
Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA
L. Wang
University of Chinese Academy of Sciences, Beijing, People’s Republic of China

Funding: U.S. Dept. of Energy
A novel Bimodal Electron Gun is designed to apply microwaves at two harmonically-related frequency in a 0.6 cell RF gun to increase the RF breakdown threshold and enhance the beam quality. This stratagem is intended to allow the RF gun structure to support a high accelera-tion gradient as well as to manipulate the emittance evolution in the half cell. By selecting a proper ampli-tude ratio and phase relationship between the first and second harmonic RF field components in the gun cavity, the superposition of the harmonic field components can provide a flat-top like RF profile to omitting the RF emittance component in the gun, while increase the RF breakdown threshold. The recent status of the Bimodal Electron Gun R&D is presented, including the designs of the novel two frequency RF structure and the simulation of the beam dynamic.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS054

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paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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TUPTS069

A Plasmonic Niobium Photocathode for SRF Gun Applications

2079

F.E. Hannon
JLab, Newport News, Virginia, USA
G. Andonian, L.H. Harris
RadiaBeam, Marina del Rey, California, USA

The typical quantum efficiency of niobium is of the order 10^-4, whilst also requiring UV lasers for emission. This paper presents the results of a plasmonic niobium surface that operates with IR laser via multiphoton emission.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS069

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPTS070

Systematic Benchmarking of a Planar (N)UNCD Field Emission Cathode

2083

J.H. Shao, M.E. Conde, W. Liu, J.G. Power, E.E. Wisniewski
ANL, Argonne, Illinois, USA
S.V. Baryshev, M.S. Schneider
Michigan State University, East Lansing, Michigan, USA
G. Chen
IIT, Chicago, Illinois, USA
K. Kovi
Euclid TechLabs, LLC, Solon, Ohio, USA
L.K. Spentzouris
Illinois Institute of Technology, Chicago, Illinois, USA

Planar nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, is a unique and attractive field emission source because of the capability to generate high charge beam, the simplicity of production without shaped emitters, and the ease of handling with moderate vacuum requirement. In the presented study using an L-band normal conducting single-cell rf gun, a (N)UNCD cathode has been conditioned to 42 MV/m with a well-controlled manner and reached a maximum charge of 15 nC and an average emission current of 6~mA during a 2.5 us emission period. The systematic study of emission properties during the rf conditioning process illustrates the tunability of (N)UNCD in a wide range of surface gradients. This research demonstrates the versatility of (N)UNCD cathode which could enable multiple designs of field emission rf injector for industrial and scientific applications.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS070

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paper received ※ 20 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPTS073

Analysis of Electron Beam Divergence in Diamond Field Emitter Array Cathodes

2090

D. Kim, H.L. Andrews, R.L. Fleming, C. Huang, J.W. Lewellen, K.E. Nichols, V.N. Pavlenko, E.I. Simakov
LANL, Los Alamos, New Mexico, USA
B.K. Choi
Cheju Halla University, Jeju-si, Republic of Korea

Funding: Los Alamos National Laboratory (LANL) Laboratory Directed Research and Development (LDRD) program (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-NA-0003525).
At Los Alamos National Laboratory (LANL), we have recently established a capability to fabricate diamond array cathodes for electron beam sources. Our fabricated diamond field emitter arrays (DFEAs) are the arrays of micrometer-scale diamond pyramids with nanometer-scale sharp tips and produce high per-tip current (> 15 μA per-tip) in DC testing. For the beam divergence measurements, we designed and assembled a test stand consisting of a DFEA cathode, a mesh aperture of 0.375-inch for an anode, and AZO (ZnO:Al2O3) screen coated on a sapphire substrate for beam visualization. A negative voltage of about 40 kV is applied to the cathode, and the mesh and the screen are kept at ground. We measure a size of the electron beam on the AZO screen at different mesh to screen distances at a fixed cathode-mesh gap in order to calculate the beam divergence angles. We also perform the beam dynamics simulations with Computer Simulation Technology (CST) Studio and General Particle Tracer (GPT) using a single pyramidal shape with a nanowire tip model. In this presentation, the measured experimental results of the beam divergences will be compared to the beam dynamic simulations.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS073

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paper received ※ 14 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPTS077

Design of a High Gradient THz-Driven Electron Gun

2098

SUSPFO127

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S.M. Lewis, V.A. Dolgashev, A.A. Haase, E.A. Nanni, M.A.K. Othman, A.V. Sy, S.G. Tantawi
SLAC, Menlo Park, California, USA
D. Kim, E.I. Simakov
LANL, Los Alamos, New Mexico, USA

Funding: This work was supported by Department of Energy contract DE-AC02-76SF00515. This work was also supported by NSF grants PHY-1734015.
We present the design of a high-gradient electron gun. The goal of this gun is to generate relativistic electrons using GV/m accelerating fields. The initial design is a standing-wave field-emission gun operating in the pi-mode with a cavity frequency of 110.08 GHz. A pulsed 110 GHz gyrotron oscillator will be used to drive the structure with power coupled in through a TM01 circular waveguide mode. The gun is machined in two halves which are bonded. This prototype will be used to characterize the electron beam and study RF breakdown at 110 GHz.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS077

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paper received ※ 14 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPTS079

Overcoming Multipacting Barriers in SRF Photoinjectors

2105

I. Petrushina
SUNY SB, Stony Brook, New York, USA
V. Litvinenko, G. Narayan, I. Pinayev, F. Severino, K.S. Smith
BNL, Upton, Long Island, New York, USA
V. Litvinenko
Stony Brook University, Stony Brook, USA

Superconducting RF (SRF) photoinjectors are considered to be a potential breakthrough in the area of high brightness electron sources. However, there is always the very important question of the compatibility of SRF cavities and high quantum efficiency (QE) photocathodes. A deposition of active elements from high QE photocathodes on the surface of a cavity makes it more vulnerable to multipacting (MP) and could affect the operation of an SRF gun. On the other side, MP can significantly reduce the lifetime of a photocathode. It is well known in the SRF community that a strong coupling, high forward power and sufficient cleanliness of cavity walls are the key components to overcome a low-level MP zone. In this paper we present a theoretical model of passing a MP barrier which could help estimate the desirable conditions for successful operation of an SRF gun. We demonstrate our results for the 113 MHz SRF photo-injector for Coherent electron Cooling (CeC) alongside with the experimental observations and 3D simulations of the MP discharge in the cavity. The results of the theoretical model and simulations show good agreement with the experimental results, and demonstrate that, if approached carefully, MP zones can be easily passed without any harm to the photocathode.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS079

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paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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TUPTS083

Simulations and Experimental Plans for a High-Repetition-Rate Field-Enhanced Conduction-Cooled Superconducting RF Electron Source

2113

SUSPFO047

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O. Mohsen, A. McKeown, D. Mihalcea, P. Piot, I. Salehinia
Northern Illinois University, DeKalb, Illinois, USA
R. Dhuley, M.G. Geelhoed, D. Mihalcea, P. Piot, J.C.T. Thangaraj
Fermilab, Batavia, Illinois, USA

Funding: Work supported by DOE awards DE-SC0018367 with NIU and DE-AC02-07CH11359 with Fermilab.
We present a novel RF design for a field enhanced electron source driven by field emission cathodes. The proposed electron source relies on the enhanced high electric field gradients at the cathode to simultaneously extract and accelerate electrons. The system will be tested in a conduction-cooled superconducting radio-frequency cavity recently demonstrated at Fermilab. In this paper, we present electromagnetic and thermal simulations of the setup that support the feasibility of the design.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS083

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paper received ※ 18 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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TUPTS084

Performances of Silicon-Based Field-Emission Cathodes Coated with UltraNano Crystalline Diamond

2117

O. Mohsen, V. Korampally, A. Lueangaramwong, P. Piot, V. Valluri
Northern Illinois University, DeKalb, Illinois, USA
R. Divan, A.V. Sumant
Argonne National Laboratory, Argonne, Illinois, USA
P. Piot
Fermilab, Batavia, Illinois, USA

Funding: Work supported by NSF grant PHY-1535401 and DOE award DE-SC0018367 with NIU
Field-emission electron sources have been considered as possible candidates for the production of bright or high-current electron bunches. In this paper, we report on the experimental characterization of silicon-based field-emitter arrays (FEA) in a DC high voltage gap. The silicon cathodes are produced via a simple self-assembling process. The measurement reported in this paper especially compares the field-emission properties of a nanostructured and planar diamond-coated Si-based cathode.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS084

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paper received ※ 17 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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TUPTS088

A Normal Conducting RF Gun as an Electron Source for JLEIC Cooling

2127

F.E. Hannon, R.A. Rimmer
JLab, Newport News, Virginia, USA

The baseline design for a magnetized injector for the bunched-beam electron cooler ring, as part of the Jeffer-son Lab Electron Ion Collider (JLEIC) uses a DC photo-cathode electron gun as the source. A challenging aspect of this concept is transporting a 3.2nC electron bunch at low energy and preserving the angular momentum. An RF gun source has been investigated to gauge the potential advantages of high gradient on the photocathode and higher exit energy. The design is presented and compared with the baseline results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS088

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paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPTS089

Observations of the Femtosecond Laser-Induced Emission From the Diamond Field Emitter Tips

2130

E.I. Simakov, H.L. Andrews, R.L. Fleming, D. Kim, V.N. Pavlenko
LANL, Los Alamos, New Mexico, USA
D.S. Black, K.J. Leedle
Stanford University, Stanford, California, USA

Funding: Los Alamos National Laboratory LDRD Program
We present the results of experimental observation of emission from single diamond field emitter tips when triggered by an ultra-short laser pulse. Diamond field emitter array (DFEA) cathodes were originally proposed for applications that require large current densities. DFEAs represent periodic arrays of diamond pyramids with micron-size dimensions and tips with diameters of the order of tens of nanometers. DFEAs are known to produce significant currents in field emission regime under direct current (DC) fields and in radio-frequency (RF) guns. It has been proposed that single diamond tip emitters can be employed for production of small tightly focused electron beams for dielectric laser accelerators (DLAs) that accelerate particles using the energy of light produced by infrared lasers. To generate short electron bunches required by DLAs diamond pyramids may be triggered with a laser. We have recently observed emission produced by a single diamond pyramid when triggered by a laser at different wavelengths from 256 nm to 2020 nm. We have conducted studies with the goal to understand mechanism of the emission. We clearly observed the change in emission mechanism when the wavelength changed from 256 nm to 512 nm. We believe that while the emission at 256 nm is a clear photoemission, the emission at longer wavelengths is likely the field emission caused by intense electric fields of the laser.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS089

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paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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TUPTS090

Experimental Results of Dense Array Diamond Field Emitters in RF Gun

2134

K.E. Nichols, H.L. Andrews, D. Kim, E.I. Simakov
LANL, Los Alamos, New Mexico, USA
S.P. Antipov
Euclid Beamlabs LLC, Bolingbrook, USA
G. Chen
IIT, Chicago, Illinois, USA
M.E. Conde, D.S. Doran, G. Ha, W. Liu, J.F. Power, J.H. Shao, C. Whiteford, E.E. Wisniewski
ANL, Argonne, Illinois, USA

We present experimental emission results from arrays of diamond field emitter tips operating in an RF gun at the Argonne Cathode Test-stand. Results from various arrays will be presented with different spacing between array elements. Very high charge densities were produced at various field gradients. The maximum field gradient for a particular geometry was discovered and break-down effects will be presented. Cathode lifetime was preliminarily studied. Further experiments are being planned and work on the cathode design optimization to produce higher quality beams will be discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS090

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPTS091

Physics of Electron Beam Generation and Dynamics From Diamond Field Emitter Arrays

2137

C. Huang, H.L. Andrews, R.C. Baker, R.L. Fleming, D. Kim, T.J. Kwan, V.N. Pavlenko, A. Piryatinski, E.I. Simakov
LANL, Los Alamos, New Mexico, USA

Funding: Work supported by the LDRD program at Los Alamos National Laboratory
Many applications such as compact accelerators and electron microscopy demand high brightness electron beams with small beam size and low emittance. Electric-field-assisted diamond emitters manufactured from semiconductor processes are strong candidates for cathodes in such sources. The micro-scale pyramid structure of the emitter has the desirable attribute of significant field enhancement at the sharp interfaces (apex and edges) to facilitate electron emission. We use the LSP particle-in-cell code to simulate the diamond emitter in a diode setup and obtain the beam size and divergence. An empirical fit of the fields around the apex is extracted for detail study. The trend of the beam divergence observed in the simulation is further corroborated using electron’s trajectory in the empirical field model.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS091

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paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPTS093

Magnetized Gridded Thermionic Electron Source

2140

SUSPFO122

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M.S. Stefani
ODU, Norfolk, Virginia, USA
C.M. Gulliford, V.O. Kostroun, C.E. Mayes, K.W. Smolenski
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
F.E. Hannon, M. Poelker, R. Suleiman
JLab, Newport News, Virginia, USA

Funding: This manuscript has been authored by Jefferson Science Associates, LLC under Contract No. DE-AC05-06OR23177 with the U.S. Department of Energy.
The study of magnetized electron beam has become a high priority for its use in ion beam cooling as part of Electron Ion Colliders and the potential of easily forming flat beams for various applications. The demand for high average current for effective ion beam cooling has caused consideration of using bunched magnetized electron beam produced by a gridded thermionic electron gun. This paper presents the design of a potential electron source for JCIEC first measurements characterizing the beam properties of a magnetized thermionic gun.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS093

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paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPTS103

The Progress of High Current High Bunch Charge Polarized Electron HVDC Gun

2160

E. Wang, I. Ben-Zvi, R.F. Lambiase, W. Liu, O.H. Rahman, J. Skaritka, F.J. Willeke
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The high current and high bunch charge polarized electron source is essential for cost reduction of eRHIC. It aims to deliver electron beam with 10 mA average current and 5.3 nC bunch charge. We analyzed the mechanism of cathode degradation and proposed using a large strain superlattice GaAs photocathode in a high voltage DC gun to increase the charge lifetime above kilo Coulomb. The gun has been designed and fabricated and expected to start commissioning by the mid of this year. In this paper, we will present the modeling of ion back bombardment and cathode degrading. We proposed an anode offset scheme to increase cathode lifetime. Also, we will describe the details of gun design and the strategies to demonstrate high current high charge polarized electron beam from this source.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS103

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paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPTS104

Spatio-Temporal Shaping of the Photocathode Laser Pulse for Low-Emittance Shaped Electron Bunches

2163

T. Xu, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
C.-J. Jing, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
P. Piot
Fermilab, Batavia, Illinois, USA
J.G. Power
ANL, Argonne, Illinois, USA

Funding: This work is supported by the U.S. DOE contract No. DE- SC0017750 with Euclid Techlabs LLC., No. DE-SC0018656 with NIU, and No. DE-AC02-06CH11357 with ANL.
Photocathode laser shaping techniques to generate temporally shaped electron bunches are appealing owing to their simplicity. Such technique is being considered to form shaped electron bunches to enhance the transformer ratio in beam-driven accelerators. At low energy (i.e. during the emission process) the transverse and longitudinal space charge effects are coupled so that attaining a low beam transverse emittance require the laser to be spatiotemporal shaped. In this paper, we explore the generation of a linearly-ramped bunch with optimized transverse emittance by temporally and radially shaping the laser pulse to provide an adequate initial distribution. We discuss a possible implementation of the optical shaping technique and describe a planned experiment.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS104

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paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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